The present invention relates to fluid detecting systems and more particularly to a stack gas analyzer system having improved calibrating and sampling subsystems.
Effluent or exhaust gases from many industrial processes must be monitored and analyzed to be certain that concentrations of certain constituents do not exceed prescribed limits. While effluent flows can be monitored by capturing an effluent sample in a sealable container and by transporting that container to one or more analyzers in a laboratory environment, more sophisticated effluent analyzers include conduits or pipes for conveying effluent directly to one or more nearby analyzers. Such fluid analyzers provide a "real-time" analysis of the effluent flow to permit the process parameters to be adjusted without delay, thereby reducing the chances that unacceptable levels of pollutants will be exhausted to the atmosphere.
The analyzers of such "real-time" systems must, of course, be calibrated periodically to ensure that the system accuracy remains at acceptable levels. In general, the systems are calibrated by supplying known concentrations of suspected effluent constituents to the analyzers to determine whether the analyzer reading corresponds to the known concentration.
One problem with known calibration systems is that the calibrating fluids are normally supplied directly to the analyzers and do not enter the analyzers through the path followed by effluent samples. Any part of a sample system can react with one or more constituents in effluent flow, causing the analyzers to read post-reaction concentrations which may not match concentrations in the main effluent flow. since the effect of sample system reactions with traversing effluent fluids is not easily determined, calibration errors in such systems are not easily eliminated.
Another problem which occurs during the use of prior calibration systems is that the calibrating operations are not necessarily performed under conditions which exist during normal effluent sampling operations. Variations in flow rates and pressures can be significant as these may affect the concentrations of constituents which ultimately reach the analyzers during calibrating or effluent sampling operations.
Still another problem which exists in prior art analyzers is that the sample supply has normally been insufficient to drive more than one or very few analyzers. Where several different analyzers were needed to detect the presence of different constitutents in the effluent, a number of sampling systems have had to be provided. This, of course, adds to the expense of installing and maintaining the entire analyzer system.